Apparatus for making tungsten carbide castings



March 22, 1938. 0'. F. MARVIN 2,112,110

APPARATUS FOR MAKING TUNGSTEN CARBIDE CASTINGS Original Filed March 19, 1932 .E jlql a) /.o ,7 AS

[NVENTOR Orr/7 $110 M ATTO R N EV Patented Mar. 22, 1938 PATENT OFFICE APPARATUS FOR MAKING TUNGS'I'EN CARBIDE OASTINGS Orrin F. Marvin, Los Angelcs, CaliL, assi'gnor to Mills Alloys, Inc., Los Angeles, Calif., a corporation of Delaware Original application March 19, 1932, Serial No.

599,938, now Patent No. 2,028,911 dated January 28, 1936. 1935, Serial No. 31,304

8 Claims.

This invention relates to a production of sharply defined cast bodies from difflcultly fusible metals, such for example, as tungsten carbide and the like, and more particularly to an improvement over the co-pending application to Oscar L. Mills for a. Tungsten carbide product and Process of making same, Serial No. 455,732, filed January 17, 1931.

This application is a division of application Serial No. 599,938, filed in my name on March 19, 1932, now Patent No. 2,028,911, issued January 28, 1936 and entitled Apparatus and process for making tungsten carbide castings.

In the above mentioned copending aplication of Oscar L. Mills a process is described for producing a cast article of manufacture from molten tungsten carbide which is characterized by a fine grained structure. In this process, a molten tungsten carbide mass is first produced at a temperature above its melting point; as for example, by the aid of the inventions disclosed in the prior patents to Oscar L. Mills, No. 1,718,- 558, issued July 2, 1929 and No. 1,721,966, issued July 23, 1929. This mass preferably has, by weight, not less than 2 percent of carbon, nor more than 6 percent thereof.

When this material is thoroughly and completely molten, as in a carbon crucible capable of accommodating at least several pounds thereof, it is poured into a mold of the desired configuration, and subjected to pressure for the purpose of securing a fine grain structure. This is accomplished by the aid of centrifugal force; which is produced by providing a rotating mold structure, which in rotating throws the molten material against the walls thereof.

I have found that a uniform and fine grained product can be obtained by the use of a double or combination mold structure, comprising essentially an inner graphite mold proper and an outer mold or support of copper or silver, with the application of pressure, as for example by centrifugal force. This double mold allows the casting to chill slowly enough in order to reduce the possibility of producing internal strains. The graphite shell comprising the mold proper is made so that it retains the heat for a sufficient period to effect this result; and this heat retention property must be enhanced by the aid of further heat insulation, as by an air space, between the copper and the graphite mold. Furthermore, the insulation acts to keep the graphite mold from transmitting heat from the cast alloy, except at a desired retarded rate, thereby retain- Divided and this application July 15,

ing this heat for the desired period and preventing unequal or deleterious or partial cooling.

Although I prefer to utilize tungsten carbide without the addition of any other element, a small percentage of free carbon or of other ma.- terial such as boron, silicon, cobalt, nickel or chromium may be employed, but only to a sparing extent, because such admixtures tend to destroy the copper parts of the mold. Such alloying materials, which of course tend materially to reduce the hardness of the product, are not essential in my process, because I secure the desired structure due to my improved treatment of the molten material.

My invention possesses many other advantages. and has other objects which may be made more easily apparent from a consideration of one embodiment of my invention. For this purpose I have shown one form in the drawing accompanying and forming part of the present specification. I shall now proceed to describe this form in detail, which illustrates the general principles of my invention; but it is to be understood that this detailed description is not to be taken in a. limiting sense, since the scope of my invention is best defined by the appended claims.

Referring to the drawing:

Figure 1 is a diagrammatic side elevation of an apparatus utilized in my invention;

Fig. 2 is a fragmentary plan view thereof;

Fig. 3 is a fragmentary detailed sectional view of a mold used in practicing my processyand Fig. 4 is a. section thereof taken substantially along the plane 44 of Fig. 3.

A molten tungsten carbide mass is first produced as by the aid of the invention disclosed by the prior Patents 1,719,558 issued July 2, 1929, and 1,721,966 issued July 23, 1929, to Oscar L. Mills. This mass is heated to a. temperature above its melting point, and has, by weight, not less than 2 percent of carbon, nor more than 6 percent thereof in the preferred form. It can be alloyed with other metals, but preferably there should not be more than 2 percent by weight of such materials or other impurities. Among such alloying metals may be mentioned the iron group, chromium, molybdenum, tantalum, boron, silicon, thorium and titanium.

When the mixture is thoroughly and completely molten, as in a carbon or graphite crucible capable of accommodating at least several pounds of the material, it is poured into a mold of the desired configuration, and subjected to pressure for the purpose of securing a sharply defined product with a fine grain structure. The

material is heated to a very high temperature; somewhere in the neighborhood of 5000 to 6000 degrees Fahrenheit, in order to put it in the plastic or fluid state.

I prefer to cast the molten material in a mold that is capable of gradually and uniformly absorbing and transferring the heat from the product. Combination molds having a refractory mold proper made from graphite and an outer surrounding copper or silver jacket or mold are admirably suited for this purpose. Graphite will not materially react with the molten mass and due to its low heat conductivity gradually absorbs and transfers heat away from the product and thus aids in producing the desired casting without internal strains. The thickness of the graphite mold is determined in accordance with the mass of the casting. In general, the larger the casting, the thicker this mold should be.

While the material is still molten, it is subjected to pressure, as hereinabove set forth. A convenient way of accomplishing this is by the aid of centrifugal force. Thus the mold structure can be so arranged that it can be rotated to throw or urge the molten mass against it and in the graphite mold proper to cast the desired sharply defined product.

I have indicated in the present instance a combination mold structure that is capable of casting a product such as a hollow cylinder; however, as will be hereinafter set forth, other sharply defined products can be cast.

The combination mold structure I 0 comprises an outer shell or mold formed of copper, silver or the like, and an inner graphite mold proper I I.

The outer mold I0 consists of a pair of hollowed out members I2 and I3 which when superimposed in abutting relationship, define a space in which the mold proper I I resides, and which forms a sprue for the passage of molten metal to the mold proper. There is a mold at each end of the member Ill. The mold proper may be confined in this space as by a pair of end members I4 formed of graphite, one at each end of member ID. Each of these end members may be provided with inwardly extending corrugations or ribs I 5 which cooperate with one end of the mold proper to define air spaces I6. A pair of rigid L-shaped metallic end members or brackets I6 and I1 abut against the graphite end members It and overlie the ends of the members I2 and I3. The rigid end members I6 and I! are rigidly secured to the outer mold ID as by bolts I8 and I9 extending therethrough and into the channel member I3 in order to prevent the graphite end members I4 from becoming displaced or discharged during rotation of the mold. This outer mold, as thus far described, is rigidly secured to a heavy metallic support or base 20 as by bolts 2I and 22.

The top member I2 of the outer mold can be made relatively immovable with respect to the lower member I3 as by a pair of hooks 23. The hooks 23 cooperate with lugs 24 formed on the sides of the top member I2, and the legs thereof extend downwardly through openings 25 in the supporting member 20. A pair of interconnecting levers 26 are pivotally secured at one end to the ends of the legs of the hooks 23.as at 21, and are also pivotally secured at an intermediate point to a pair of depending lugs 28 formed integral with the base 20. It is apparent that by a single downward movement of the levers 26, the hooks 23 will be lifted upwardly out of engagement with the lugs 24 and permit the relative movement and separation -of the top member I2.

The upper member I2 can have a large central aperture 23 to permit the pouring of the molten material into the closed outer mold, which is rotated about a vertical, central axis, in order to throw the material under pressure into the mold proper II. The pressure thus attained may be of the order of 0 to 200 pounds per square inch, although higher or lower values could be used. The lower member l3 can have a large saucerlike depression 30 in the top face thereof immediately below the aperture 23 in order to permit the molten material poured in to accumulate therein.

The mold proper II is adapted to be positioned in the outer mold III in the space defined by members I2 and I3, one at each end thereof, although it is readily apparent that more than one can be so positioned by simply changing the inner contour of the outer mold. The mold proper is formed completely of graphite and is shown in this instance as comprising a. hollow tubular shell 3| having upstanding end portions or flanges 32 and 33 which abut against the inner periphery of the members I2 and I3. The shell 3| is made of the right thickness to assure a gradual but not too slow cooling of the molten material. In order to prevent the sagging or breaking of this shell in case it is made from thin material, reinforcing wire strands 34 can be wound therearound, and a graphite ring 35 is inserted between the shell and the outer mold intermediate the ends of the former. The air space 3 I between the shell and outer mold serves as a heat insulation and thus further aids in preventing the quick chilling of themolten mass.

Rear and forward graphite end members 36 and 31 respectively, are inserted in inner peripheral recesses formed in the sleeve 3|, and a graphite core 38 extends through these end members and serves to define therewith and with the inner periphery of the shell a space in which the material is to be cast. The end member 36 as well as the flange 32 abut against the tips of the ribs I5 and form with the members I4 the air spaces I6. These spaces serve as heat insulation spaces to prevent the quick transmission of heat from the mold proper to the copper portions I2, I3.

The forward end member 31 is provided with gates or ports 39 through which the molten material is forced into the space defined by the mold proper upon rotation. Both of the end members may be provided if desired with central recesses 40 and 4| which provide a space for the formation of bosses on the ends of the cylinder to be cast.

It is apparent that the mold proper I I is inserted in the outer mold I0 prior to the pouring in of the molten material. This can be accomplished by removing member I2 in a manner already outlined.

To provide the above mentioned rotation, I show in this instance a shaft 42 joined to the bottom of the base 20, that can be rotated by any source of motion. For example, in Fig. 1, I show shaft 42 supported in a bracket structure 43 on table 44, and an electric motor 45 conveniently supported under the table, which drives the shaft.

A product, such as a cylinder, formed in the manner above described, is permitted to remain in the mold proper for a. short interval of time to permit the gradual and uniform cooling thereof, Usually this interval is attained by the necessary delay incident to the opening of the mold. As hereinabove set forth, the arrangement of a. combination mold in the manner and of materials described, assures the gradual, but not too slow, removal of heat from the product. When the product has assumed a self-sustaining form, it is placed in a space where it is still further gradually cooled. This can be accomplished by removing member II in the manner described.

A space for gradually cooling the product to room temperature can be formed by a box 46 that contains some powdered material that retains heat long enough to insure slow cooling. For example, a mass of silica fiour 41 can be used in box 46. If desired, the sides and bottom of the container can be provided with a layer of heat insulating material. This slow cooling effectively prevents internal strains.

By proper choice of the relative dimensions of the mold I I and the outer casing l2--l3, the rate of cooling can be predetermined. Thus the air spaces I6 and 3| can be made of proper size, as well as the area of contact between the annular surface of flanges 32, 35, 33 and the inner surface of the structure l2--l3 can be made to fit the requirements. In fact, those annular surfaces of contact can be multiplied or reduced in accord with these requirements.

I claim:

1. A mold for casting sharply defined castings from highly refractory difilcultly fusible metallic material, comprising an inner graphite mold proper and an outer mold surrounding said mold proper and spaced therefrom, said outer mold comprising a pair of hollow members, and means forming an opening in one of said members for the introduction of the molten material.

2. A mold for casting sharply defined castings from highly refractory difficultly fusible metallic material, comprising an inner graphite mold proper and an outer mold surrounding said mold proper and spaced therefrom, said outer mold comprising a pair of members, means forming an opening in one of said members for the introduction of the molten material, said mold proper comprising a shell having end members, and means forming gates in one of said end members for the entry of the molten material into said mold.

3. A mold for casting sharply defined castings from highly refractory difllcultly fusible metallic material, comprising an inner graphite mold proper and an outer mold surrounding said mold Proper, said outer mold comprising a pair of members, means forming an opening in one of said members for the introduction of the molten material, said mold proper comprising a shell 50 having end members, supports for said shell, and

means forming gates in one of said end members for (the entry or the molten material into said mol 4. A mold for casting sharply defined castings from highly refractory difilcultly fusible metallic material, comprising an inner graphite mold proper and an outer mold surrounding said mold proper and in limited heat exchange relation thereto, said outer mold comprising a pair of members, means forming an opening in one of said members for the introduction of the molten material, said mold proper comprising a shell having end members, means forming gates in one of said end members for the entry of the molten material into said mold, a rotatable support for said outer mold, and means for rapidly rotating said outer mold to urge the material under pressure into said mold proper.

5. A mold for casting sharply defined castings from highly refractory difiicultly fusible metallic material, comprising an inner graphiite mold proper and an outer mold surrounding said mold proper and spaced therefrom, said outer mold comprising a pair of members, means forming an opening in one of said members for the introduction of the molten material, said mold proper comprising a shell having end members, supports for said shell, means forming gates in one of said end members for the entry of the molten material into said mold, a rotatable support for said outer mold and means for rapidly rotating said outer mold to urge the material under pressure into said mold proper.

6. A mold for casting sharply defined castings from highly refractory, diiilcultly fusible metallic material, comprising an inner graphite mold proper, and an outer mold having an internal surface supporting said inner mold and projecting beyond the mold to form a sprue for molten material to be passed into the mold proper.

7. A mold for casting sharply defined castings from highly refractory, difficultly fusible metallic material, comprising an inner graphite mold proper, an outer mold having an internal surface supporting said inner mold and projecting beyond the mold to form a sprue, a rotatable support for the outer mold, means permitting introduction of molten material into said sprue while said mold is being rotated, and means for rapidly rotating the outer mold to urge said molten material along the sprue and into the mold proper under pressure.

v8. In a device for casting a carbide of the chromium group, a mold of carbon material, and means forming an outer enclosure for the mold, said mold and enclosure having a limited area of contact with each other, said area being determined to fix the rate of heat transfer from the cast article through the enclosure, a rotatable support for the outer enclosure, and means to rotate the outer enclosure, said outer enclosure having means to which pre-molten carbide is adapted to be passed during rotation of the enclosure.

ORRIN F. MARVIN. 

